1. Field of the Invention
This invention relates to nonaqueous acrylic resin dispersions and particularly to acrylic resin plastisols and organosols. This invention also relates to acrylic resin dispersions containing photopolymerizable ethylenically unsaturated compounds.
2. Description of the Prior Art
Certain polymeric resin dispersions referred to as plastisols are fluid mixtures, ranging in viscosity from pourable liquids to heavy pastes, obtained by dispersing polymeric resin particles in nonvolatile, nonaqueous liquid plasticizers, i.e., materials which are compatible with the polymer or resin and increase its workability and flexibility but are not solvents for the polymeric resin under ordinary conditions of storage. When the plastisol has been formed into a desired shape, e.g., by molding or coating, it can be heated to coalesce the polymeric resin particles and the nonvolatile liquid constituent, thereby forming a homogeneous mass. Theoretically, by appropriate choice of ingredients, any polymeric resin can be made into a plastisol. In practice, however, both the commercial use and the technical literature have focused almost exclusively on the use of polyvinyl chloride in forming plastisols, to the extent that "plastisol" is cross-referenced to "polyvinyl chloride" in Chemical Abstracts and in many textbooks plastisols are described as suspensions of polyvinyl chloride resin. Volatile diluents can be added to plastisol dispersions to modify their viscosity and to achieve desirable handling characteristics in coating or other forming operations. When the dispersion contains no more than 10% volatile diluent, it is still regarded as a plastisol; when the volatile diluent content exceeds 10%, however, the dispersion is regarded as an "organosol", H. A. Sarvetnick, "Plastisols and Organosols", Van Nostrand Reinhold Company, New York (1972), page 201.
Polyvinyl chloride plastisols are known wherein the polyvinyl chloride is copolymerized with other monomers, including acrylic monomers, that constitute a minority (&lt;35% by weight) of the polymer composition. In U.S. Pat. No. 2,618,621 there are disclosed polyvinyl chloride plastisols wherein part of the plasticizer content is replaced with an acrylic monomer, which is then conventionally thermally polymerized at the temperature encountered in the step of coalescing the polyvinyl chloride resin. French Pat. No. 73.06503 discloses plastisols prepared from a variety of polymers, primarily of the styrene family, with the requirements that the polymers be multiple phase and that they be dispersed in polar plasticizers.
It has now been found possible to prepare plastisols based on acrylic polymers that are amenable to a variety of forming techniques with all of the economic, ecological, health and safety advantages attendant on solvent-free operation. The acrylic resin compositions may be either plastisols or organosols, depending on the amount of volatile diluent included, if any.